During a planting period of corn, etc., triazine-containing herbicides such as atrazine and acid anilide-containing herbicides such as alachlor and metolachlor have been conventionally used. However, atrazine shows low efficacy to gramineous weeds, while alachlor and metolachlor show low efficacy to broad-leaved weeds. It is therefore difficult at the present times to control both of gramineous weeds and broad-leaved weeds at once using a single herbicide. Further, the use of these chemicals in combination does not give any sufficient effect. Moreover, the above herbicides are undesirable in view of an environmental problem due to their high dosage requirement.
On the other hand, it is known that specific benzoylcyclohexanedione derivatives have herbicidal activity (see JP-B-1-30818, JP-A-61-155347, JP-A-1-143851, JP-A-3-120202, EP 135,191A, EP 186,118A, EP 186,119A, U.S. Pat. No. 4,954,165, GB 2,215,333A, EP 336,898A, U.S. Pat. No. 4,937,386, U.S. Pat. No. 4,780,127, U.S. Pat. No. 5,092,919 and PCT International Publication. 90/05712). Typical examples of the benzoylcyclohexanedione derivatives disclosed in the above Publications are as follows. ##STR2##
Further, JP-A-64-6256 discloses that cyclohexanedione derivatives having a fused bicyclic group containing heteroatoms exhibit herbicidal activity. ##STR3##
However, cyclohexanedione derivatives having a thiochroman ring such as compounds of the present invention are not known yet.
Further, the cyclohexanedione derivatives that have been already disclosed are insufficient in practical use, particularly poor in herbicidal activity to gramineous weeds such as barnyardgrass and green foxtail.